function foo(n:1|2|3){
    switch (n){
        case 1:
            break;
        case 2:
            break;
        case 3:
            break;
        default:
            break;
    }
}

foo(1)

//any任何类型
let a:any = 'he';
a = 123
a = true
a.map(()=>{})

//unknown ，ts默认会进行检测
let b:unknown = 'he';
b = 123
//b.map(()=>{})
